Power amplifiers used in GSM/GPRS/EGPRS cellular handsets are designed to operate from a battery that provides a typical power supply voltage of 3.6 volts, Unfortunately, using the same power amplifier in a PC card application is problematic since the power supply voltage is nominally 3.3 volts for PC cards. The lower operating voltage of the PC card makes it very difficult to meet the requirement for an 8-PSK transmit modulation spectrum at maximum output power as defined in the GSM 05.05 cellular telephony specification. This particular problem has been resolved by designing a step-up DC-to-DC converter to boost the voltage at the power amplifier to 3.6 volts.
Boosting the power amplifier supply voltage to 3.6 volts works well when a PC card is operating in EDGE mode due to lower transmit output power requirements. However, when a PC card is operating at higher output powers like those required for GMSK modulation modes, the inefficiency of the step-up DC-to-DC boost converter results in a violation of the PCMCIA current consumption specification. Additionally, GMSK modulation is a constant envelope and the power amplifier is run saturated. Thus, it is not necessary to boost the power amplifier supply voltage.
What is needed is a means for optimizing power amplifier performance in lower power supply voltage PC card applications to allow for efficient operation in both the 8-PSK and GMSK modulation modes for GSM data exchange standards such as GPRS and EDGE.